Technical Field
The instant disclosure relates to a field of earphone and, more particularly, to an earphone device having a concentrating tube.
Related Art
Conventional earphones perform electro-acoustic conversions by moving coil drivers. The moving coil driver includes a voice coil, a permanent magnet, and a diaphragm. When audio signals are transmitted to the voice coil by an audio line, the voice coil generates a magnetic field based upon electromagnetic induction. The diaphragm is vibrated by the interaction of the magnetic field generated by the electromagnetic induction and the magnetic field generated by the permanent magnet, and the audio signals are converted into acoustic waves for outputting.
The audio signals include a part of low frequency and a part of high frequency. The part of low frequency and the part of high frequency have different characteristics in terms of frequency response. According to prior techniques, the parts of low frequency and the high frequency are processed by electro-acoustic conversions through the single diaphragm; however, it is hard to produce clear sound by the single diaphragm due to different characteristics of frequency response. Distortion may occur during the electro-acoustic conversions, which results in outputted sound being unclear. Although two moving coil drivers can be adopted in an earphone to resolve the issue by having the two drivers respectively generate acoustic waves of high frequency and low frequency via a frequency dividing circuit, this increases the size of the earphone, making it unsuitable for use.
In addition, the pressure of gas inside the earphone directly affects the vibration of the diaphragm and consequently affects the frequency response thereof. When the diaphragm vibrates due to the pressure of gas inside the earphone being greater than that of gas outside the earphone, the vibration of the diaphragm is restrained by the gas with greater pressure, meaning that the amplitude of vibration of the diaphragm is depressed. As a result, certain frequency range(s) of sound that the earphone should generate, is lost.